Antimicrobial susceptibility changes and T-OMP shifts in pyrithione-passaged planktonic cultures of Pseudomonas aeruginosa PAO1

Abstract

Aims: The aim of this study was to determine whether passaging Pseudomonas aeruginosa PAO1 with sub-MICs of the pyrithione biocides results in both the induction of decreased susceptibility towards these antimicrobials and associated outer membrane profile changes. Methods and Results: Previous work by this group has shown that it is possible to induce susceptibility changes towards the isothiazolone biocides in Ps. aeruginosa PAO1 by successive passages in the presence of increasing sub-MICs of biocide. This procedure was accompanied by the loss of a 35 kDa outer membrane protein, T-OMP. In this experiment, this process was repeated with the biocides sodium pyrithione (NaPT), zinc pyrithione (ZnPT) and cetrimide. The pattern of susceptibility was similar to that observed with the isothiazolone biocides. Upon removal of biocide, the observed MIC did not return to the original pre-exposure value. The onset and development of resistance was accompanied by the loss of T-OMP from outer membrane profiles, which suggests that this is a non-specific membrane channel whose production within the cell is sensitive to biocide presence. The T-OMP reappeared when the cells were passaged in the absence of pyrithione. Cross-resistance studies indicated that induced resistance to one biocide yields partial resistance towards other members of the group and the positive control. Conclusions: These results indicate that the pyrithione biocides have similar susceptibility profiles in Ps. aeruginosa to those exhibited by the isothiazolones, but that the acquired changes in susceptibility to the pyrithiones is largely irreversible. Significance and Impact of the Study: This study indicates that acquired susceptibility changes towards sub-MICs of selected biocides are multifactorial in nature.

Pseudomonas aeruginosa PAO1 adapted to 2-phenoxyethanol shows cross-resistance to dissimilar biocides and increased susceptibility to antibiotics

“…The MIC changed from 4 to 8 and 60 to 69 g/mL, respectively. However, Abdel Malek et al (2002) reported ZnPT induced resistance to increase MIC to 25 g/mL from an initial value of 4 g/mL. In that study ZnPT resistance resulted in cross resistance towards NaPT and caused the MIC of NaPT to change from 30 to 115 g/mL.…”

“…Biocide resistance in bacteria is known to involve several mechanisms (Loughlin et al 2002;Abdel Malek et al 2002, 2009Russell 2003) thus when a small increase in MIC is observed it indicates the possible disabling of one biocide target (Gilbert and MacBain 2001). Cross-resistance to BIT on the other hand, showed significant (p < 0.05) three-fold increase in the MIC from 32 to 85 g/mL (Table II).…”

“…PE adaptation experiments were performed according to Winder et al (2000) and Abdel Malek et al (2002). Briefly, fresh P.a.…”

“…Pellets were used for OM preparations (Pugsley et al 1986). SDS-PAGE analysis was performed according to Winder et al (2000) and Abdel Malek et al (2002). Briefly, OMs were resuspended in 100 L of Tris-HCl buffer (pH 7.4).…”

“…Adaptation of P.a. to disinfectants by serial passage in increasing concentration of biocides is well documented (Loughlin et al 2002;Abdel Malek et al 2002;Winder et al 2000). The presence of constitutive and inducible efflux mechanisms removing a huge range of antimicrobials from the cell has been detected in P.a.…”